what choke setting?

[atr]

I want to shoot rifled slugs in my old mossburg bolt action 20 GA x 3" chamber. It has a variable choke settings; full, modified and improved. My question: what setting should I set the choke for shooting rifled slugs?
best
atr

[BLAHUT]

Cylinder or as close as you can get to that ??

[TNsailorman]

The most open setting on the choke tube.

[stubshaft]

+1 - The most open choke available.

[atr]

thanks guys
best
atr

[turtlezx]

just dont back it off too far or the fingers can break off